I have a 99 Volvo S80 Turbo. The check engine light was on and it was saying it was an 02 sensor bank 1 sensor 2. The car ran excellent before I replaced the 02 sensor. I replaced the 02 sensor with a universal one and had to splice wires for it to work. After that the car ran good for a day. The next morning the car ran very bad. It idled rough and the check engine light remained on. While driving the car it barley exceeded 30 mph and was very sluggish. It has a lot of trouble going up hills. I thought the problem was the catalytic converters so I went ahead and replaced them. One cat was clogged up and the other wasn't. I thought that would fix the problem however it didn't. Now the check engine light has multiple codes including a cylinder 3 misfire. My next step was to replace the plugs. I noticed three of the 6 were fouled out and replaced them. This still didn't work. I was told at Volvo that it was because I used a universal 02 sensor. They told me that I needed to replace all 4 and use a Bosch replacement. I don't want to waste anymore money and need some advice. Any help on the matter would be greatly appreciated.

A couple corrections and things that need to be added to my previous post. I used a Bosch replacement 02 sensor NOT a universal one. I remember I took that back. Also when I replaced the cat only one was clogged and when I changed the plugs only 3 on one side were fouled out. I noticed now too that I have a different 02 sensor code than I had before. Not it's saying a bank 1 sensor 1 and a random misfire. I'm starting to think it may have jumped timing. Anyone have any ideas? Thanks

Sounds to me that the O2 sensors are your issue. Perhaps you changed the wrong one by mistake. Bank 1, Bank 2, Sendor 1, Sensor2.
And then again, maybe you spliced the wrong wires. Start with these sensors bank 1-sensor 1; Bank 2-sensor1

People are still saying it's an o2 sensor issue? Would an o2 sensor issue really make a catalytic converter clog and make 3 plugs foul out? If so then maybe I won't do anything else than change all 4 02 sensors.

your computer is kicking a o2 code because the o2 sensor it detecting the extra fuel in the exhaust. The extra fuel is what clogged the cat and fouled the plugs. You might start by looking for a vacuum leak by spraying carb cleaner on them and look for eng to surge. if it surges then you found the leak if not then no leak and look at the MAP sensor. They are common to go bad so I've noticed with other people.

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